1. Field of the Invention
This invention relates to methods of and apparatus for ultrahigh frequency starting of high intensity discharge (HID) lamps. Accordingly, it is a general object of this invention to provide new and improved methods and apparatus of such character.
2. General Background
Several different circuits, commonly used to ballast and to start HID lamps, have been described by J. F. Waymouth, "Electric Discharge Lamps", The MIT Press, Cambridge and London, 1971.
The circuits described therein usually have two functions during the starting phase: they promote a breakdown condition to initiate lamp starting and then they supply adequate energy to enable the transition from a glow phase to a final arc stage. In order to start most HID lamps, however, these functions should be separated, and therefore, a starting aid was usually added to a lamp ballast. In some types of HID lamps it was necessary to enhance starting by external ionization or by pulse injection through a third electrode. HID lamps may be started, or started and operated, by high frequency pulses. Y. Koshima et al., "Stable High Frequency Operation of HID Lamps and Their Ballast Design", presented at the 1983 CIE conference (Amsterdam), for example, report stable operation of HID lamps at radio frequencies (RF), although unstable phenomena are often encountered which may trigger undesirable acoustic resonances. These resonances have been overcome by frequency modulation, as reported by R. P. Bonazoli and F. W. Paget, "Anti-Acoustic Resonance Drive for HID Electronic Ballast", Report No. 761018 (Oct. 14, 1976), Lighting Products Group, Salem, Mass., GTE Sylvania, or by superposition of higher harmonics, as reported by Koshima et al., supra.
J. Lester and S. Cohen, "The RF Starting and its Application to Miniature Metal Halide Lamps", presented at the 1985 IES conference (Detroit), reported the utilization of 40 kHz RF power, a low frequency (LF), with 3-4 kV amplitude to initiate a discharge in 100 W Metalarc lamps. Its RF starter supplied enough energy to facilitate the glow to arc transition. The lamp operation was then maintained by a conventional ballast at 60 Hertz. The RF starter continued to operate, however, after lamp starting, thus causing power line noise during the on-state period of the lamp. In order to reduce this effect, a transistor, placed in series with the starter, lowered the output voltage after 5 to 15 minutes of operation. Alternatively, a broadband differential filter between the RF starter and the power line was used to reduce line noise.
Neither of the foregoing prior art circuits completely eliminated the line noise problem, and thus the need was created for a new starter for 100 W Metalarc lamp. A modified HPS (high pressure sodium) starter, marketed under the "Advance" brand name, is presently used to ignite these lamps. Starting aids based on the bimetal pulser have also been suggested by J. Lester, "Le Theorie de Bimetal", Report No. 830411 (Apr. 4, 1983), Lighting Products Group, Salem, Mass., GTE Sylvania. Very successful results in starting and hot restarting of many types of HID lamps have been achieved with spiral line, high voltage generators, as indicated by J. M. Proud, L. A. Riseberg, and C. N. Fallier, Jr., "Method and Apparatus for Starting High Intensity Discharge Lamps", U.S. Pat. No. 4,325,004, issued Apr. 13, 1982, and by C. N. Fallier, Jr. and J. M. Proud, "Pulse Injection Starting for High Intensity Discharge Metal Halide Lamps", U.S. Pat. No. 4,353,012, issued Oct. 5, 1982.
As discussed therein, the high frequency, high voltage pulses are produced every half cycle of the line voltage and are discontinued as soon as the lamp voltage level drops to the arc value. A typical high voltage pulse generated by the spiral line has an amplitude of a few kilovolts and a width of about 0.5 .mu.s and is followed by rapidly decaying high frequency oscillations of about 1 MHz. The number of such pulses is determined by the time constant of the circuit and may be selected to optimize starting of a particular type of HID lamp, as set forth by co-pending patent application of W. W. Byszewski, C. N. Fallier, Jr. and J. N. Lester, "Multipulse Starting Aid for High-Intensity Discharge Lamps", (Docket No. 86-3-053), United States patent application, Ser. No. 07/000495, filed Jan. 5, 1987. The amplitude and width of the pulses may be varied over a wide range to meet the starting (and hot restarting) requirements of most HID lamps, as set forth in U.S. Pat. No. 4,484,085, by C. N. Fallier, Jr. and J. M. Proud, entitled "Spiral Line Voltage Pulse Generator Characterized by Secondary Winding", issued Nov. 20, 1984, and by a co-pending patent application filed by C. N. Fallier, Jr. and J. N. Lester, "Method and Apparatus for Starting High Intensity Discharge Lamps, (Docket No. 85-1-151) U.S. patent application, Ser. No. 812,577, filed Dec. 23, 1985.
Electrodeless HID lamps have been started and operated by ultrahigh frequency (915 MHz) power sources, as reported by P. O. Haugsjaa, R. J. Regan and W. H. McNeill, "Electrodeless Light Source", in U.S. Pat. No. 3,993,927, issued Nov. 23, 1976. The lamp impedance during the starting phase and during operation is matched to the power source by switchable circuits described in U.S. Pat. Nos. 3,943,401 and 4,002,944, thereby improving lamp startability.
Several patents such as U.S. Pat. Nos. 4,041,352 and 4,247,800 describe additional assistance in starting processes by ultraviolet (UV) radiation or radioactive material radiation, respectively. Very strong effects of UV radiation on the starting process have also been observed in electroded, ballast operated, HID lamps, and utilization of this effect has been suggested by J. M. Proud, W. W. Byszewski, and C. N. Fallier, Jr., "Arc Discharge Lamp with Ultraviolet Enhanced Starting Circuit", (Docket No. 24,987) in their co-pending U.S. application, Ser. No. 686,975, filed Dec. 27, 1984.
The optimum breakdown condition in a particular gas is described in detail by S. C. Brown, Introduction to Electrical Discharges in Gases, J. Wiley & Sons, Inc., New York (1966), and by A. D. MacDonald, Microwave Breakdown in Gases, J. Wiley & Sons, Inc., New York (1966). U.S. Pat. No. 3,943,401, issued Mar. 9, 1976 to P. O. Haugsjaa, R. J. Regan, and W. H. McNeill, is entitled, "Electrodeless Light Source Having a Lamp Holding Fixture Which has a Separate Characteristic Impedance for the Lamp Starting and Operating Mode".
U.S. Pat. No. 4,002,944 issued Jan. 11, 1977 to W. H. McNeill, P. O. Haugsjaa, J. M. Lech, and R. J. Regan is entitled, "Internal Match Starter for Termination Fixture Lamps".
U.S. Pat. No. 4,041,352, mentioned above, was issued Aug. 9, 1977 to W. H. McNeill, P. O. Haugsjaa, J. Lech and R. J. Regan, entitled, "Automatic Starting System for Solid State Powered Electrodeless Lamps".
U.S. Pat. No. 4,247,800, also mentioned hereinabove, issued Jan. 27, 1981 to J. M. Proud, R. J. Regan, P. O. Haugsjaa, and D. H. Baird, "Radioactive Starting Aids for Electrodeless Light Sources".
With one exception, the foregoing cited patents and patent applications have been assigned to the assignee of this application: GTE Laboratories Incorporated. Patent application Ser. No. 812,577 has been assigned to a related company.